What is difference between save and saveOrUpdate or
Difference between save and persist are common
interview question in any Hibernate interview, much like Difference
between get and load method in Hibernate. Hibernate Session class
provides couple of ways to save object into database by methods like save, saveOrUpdate and persist.You can use either save(),saveOrUpdate() or persist() based upon
your requirement for persisting object into Database.
Along with Spring
framework Interview questions, Hibernate questions are also quite popular on
J2EE interviews because of its status as leading ORM. It’s good to prepare some
questions from Hibernate before appearing in any J2EE
interviews. One of them is Difference
between save , saveOrUpdate and persist, which we will see in this
Hibernate article.

Difference
between save and saveOrUpdate in Hibernate

Main difference between save and saveOrUpdate method is that save() generates
a new identifier and INSERT record into database
while saveOrUpdate can either INSERT or UPDATE based upon existence of
record. Clearly saveOrUpdate is more flexible in terms of use
but it involves an extra processing to find out whether record already exists in
table or not.

In summary save() method saves
records into database by INSERT SQL query, Generates a new identifier and
return the Serializable
identifier back.

On the other hand saveOrUpdate()
method either INSERT or UPDATE based upon existence of object in database. If
persistence object already exists in database then UPDATE SQL will execute
and if there is no corresponding object in database than INSERT will run.

Difference between save and persist method in Hibernate

In last section we saw What are difference between save and saveOrUpdate and now we
will see Difference on save vs persist method.

1)First difference between save and persist is
there return type. Similar to save method persist also INSERT records into database
but return type of persist is void while return type of save is Serializable
object.

2) Another difference between persist and save is that both methods make
a transient
instance persistent. However, persist() method
doesn't guarantee that the identifier value will be assigned to the persistent
instance immediately, the assignment might happen at flush time.

3) One more thing which differentiate persist and save method in
Hibernate is that is there behavior on outside of transaction boundaries. persist() method guarantees
that it will not execute an INSERT statement if it is called outside of transaction
boundaries. save() method does not guarantee the
same, it returns an identifier, and if an INSERT has to be executed to get the
identifier (e.g. "identity" generator), this INSERT happens
immediately, no matter if you are inside or outside of a transaction.

4) Fourth difference between save and persist method in
Hibernate is related to previous difference on save vs persist. Because of its
above behavior of persist method outside transaction boundary, its useful in
long-running conversations with an extended Session context. On
the other hand save method is not good in a long-running conversation
with an extended Session context.

These were some differences between save, saveOrUpdate and persist method
of Hibernate. All three method are related to saving Object into database but
there behavior are quite different. Knowledge of save, persist and saveOrUpdate not only
helps to decide better use of Hibernate API but also help you to do well in
Hibernate interviews.

One more difference I would like to mention persist has to be used when cascade = cascadeType.PERSIST, If you will use save it will throw error as Exception in thread "main" org.hibernate.TransientObjectException: object references an unsaved transient instance - save the transient instance before flushing: